The present invention generally relates to a method of measuring a liquid. More particularly, the invention relates to a method of measuring a liquid wherein a "fuzzy" inference is effected based on an observed or measured quantity, and/or a quantity derived from the measured quantity, and the invention relates to an improvement of measuring accuracy, expansion of a measuring range and a decrease in time of measurement by sequentially varying a flow velocity of a substance to be measured using the fuzzy inference(s).
Fuzzy control is discussed by E. H. Mamdani in a technical article entitled "Application of Fuzzy Algorithms for Control of a Simple Dynamic Plant " appearing in the Proceedings of IEEE, vol. 121, 1974 at pages 1585-1588 and by L. A. Zadeh in a memorandum entitled "Theory of Fuzzy Sets", Memo No. ERL-M502, Electronic Research Lab., University of California, Berkeley (1975).
The present invention also relates to a liquid measuring mixer for producing a new mixed liquid by intermixing a variety of raw liquids after measuring these liquids.
Further the present invention generally relates to a liquid measuring mixer for adjusting a new mixed liquid by intermixing multiple raw liquids after measuring the raw liquids, and more particularly, to a liquid measuring mixer for precisely and efficiently measuring and intermixing the raw liquids over a wide range of measurement.
A detecting method in the measurement of liquid involves the use of a weight system (e.g., a load cell), a pressure system, (e.g., a differential pressure transmitter), a volume system (e.g., an oval flowmeter) and a variety of other systems.
In all these systems, however, measurement control is performed on condition that the flow velocity is invariable. The measurement controlling system of the closed loop in which the flow velocity is successively varied does not come under the above-described concept.
To increase the accuracy of the measurement, the following techniques have heretofore been utilized.
(1) The first technique (e.g., as shown in Japanese Patent Publication No. 148019/1981) is as follows: The flow velocity changes at two states, and the measurement is made by a change-over to the slower flow velocity in the vicinity of the measurement set value.
EXAMPLE 1. Two kinds of devices having different flow velocities are provided the change-over is executed when the deviation between the measurement set value and the actual measurement value reaches a given conditional value. PA1 EXAMPLE 2. A single device for changing-over the flow velocity to two kinds of fixed conditions is provided and the change-over is executed, as in Example 1, when the deviation reaches the given conditional value. PA1 EXAMPLE 3. Based on the contents of Examples 1 and (2), the conditional value for commanding the change-over is modified from the result of the previous actual measurement by adding a learning function identified as a software function. PA1 EXAMPLE 1. The measurement stops when the deviation between the measurement set value and the actual measurement value reaches the given condition. PA1 EXAMPLE 2. The situation is almost the same as that in example 3 of the first technique. However, the conditional value for commanding the halt of measurement is modified by performing arithmetic based on the preceding actual measurement result. PA1 (1) Conventional measurement control is effected on condition that the flow velocity is constant. The flow-rate characteristics of the valve vary depending upon the head difference, the liquid material properties or the like. As a result, the measuring accuracy is deteriorated. PA1 (2) An apparent fluctuation-width is to some extent created in the observed quantity because of dynamic characteristics of the detector, thus causing a decline of measuring accuracy. PA1 (3) In connection with the flow-rate characteristics of the valve, it is difficult to have constant and linear characteristics. The flow-rate characteristics differ according to the type of valve and the system structure. For this reason, adjustment is required for every structure to attain highly accurate measurement with a reasonable degree of certainty.
(2) The second technique (e.g., as shown in Japanese Patent Laid-Open No. 29114/1982) is as follows: There is an inflow quantity (also referred to as a head quantity) functioning as a measurement stopping condition, and the measurement technique is such that the measurement is previously stopped in anticipation of the inflow quantity.
In the above-described measurement control methods, the change-over is carried out by making the flow velocity constant or by varying the velocity at two stages. However, in such measurement control the measurement is fixed within a certain range. Therefore, the following problems are inherent.
(1) Unreliable Measuring Accuracy: A situation where the accuracy is not assured is brought about due to fluctuations in flow velocity which are caused by disturbances and variations in liquid material property (viscosity or the like). In the case of gravity transfer, fluctuations in flow velocity are created in the measurement substance which flows out depending on residual quantities (the amount of residue i.e. head difference) of the measurement substance existing in the supply containers (or tanks), or the supply container located at an upper stream side. If the head difference is large, however, the flow velocity exceeds a certain range, and the accuracy is thereby reduced. This effect also results in restriction of variation-width of the head in the container. In order to keep the head difference within a predetermined conditional range, it is strictly required that the measurement be stopped, or alternatively that the container be properly supplied with more raw material (measurement substance) to keep the supply constantly above a predetermined quantity, which results in a loss of raw material as well as an increase in production cost.
(2) Narrow Measuring Range: Since the flow velocity is restricted, a ratio of a measurable minimum measurement value to a measurable maximum measurement value is approximately 1:5. In a flow velocity 2-stage setting type, the ratio is approximately 1:10 at a maximum. The reason why the measurement range is narrow is as follows. Even if the measurement is halted, there will be an inflow quantity associated with a delay in response of the system. This inflow quantity is determined by the flow velocity. Hence, if the measurement set value is small, the inflow quantity exceeds a guaranteed scope of accuracy, and it follows that the measurement range is restricted. In production plants which deal with a wide variety of materials, there is included such a type that the ratio within the measurement range exhibits about 1:100 at maximum in the case of the same raw material. Therefore, it is necessary to select the measuring devices within a range of measurement set value. In other words, the allowable inflow quantity is assured by narrowing the measuring range under such a condition that the flow velocity is constant. Where the same kind of liquids are measured, and/or if the measurement set values are greatly different, measuring devices having proper measuring ranges are needed, which arrangement results in an increase in the number of devices.
(3) Lack of Control of Measuring Time: Measuring time depends on the measurement set value. If the measurement set value is small, the measuring time is short, and vice versa. Further where the measurement set value is small, an operating time of the system is erratic or scattered, whereby the measuring accuracy is not assured. This effect also leads to a narrower measurement range. In light of the entire system for producing new forms by intermixing multiple already-measured substances, production capability is determined by the measuring time. Especially in a pipeless transfer production system carrier capability is limited. That is, to satisfy a given production capacity, more measuring devices will be required due to a long production cycle.
For the above-described reasons, the conventional liquid measuring mixer includes a multiplicity of independently controlled measuring devices installed for every supply container. These measuring devices are also provided for optimum measuring time in view of any restriction of production capability. As a result, the system becomes intricate, and a remarkable number of measuring devices are required.
Among the proposed measuring systems, as in the case of an oval flow meter, a capacity measuring system is often employed. During use of this system, the liquid has to fill the pipe. This causes such a problem that a loss of raw liquid is created.
In order to attain highly accurate measurement, the measuring device applied to the liquid measuring mixer has heretofore been confined to such a type that a flow velocity is limited, The measuring device of such a type that the flow velocity is variable could not be seen so far.
Where liquids are fed from a plurality of supply container to a piece of container, a conventional type of liquid measuring mixer is required to have the measuring devices attached to the individual supply containers.
For instance, when adopting a capacity measuring system, as illustrated in FIG. 16, two measuring devices c. d are employed for two kinds of liquids e.g. liquids A and B in different containers a, b, respectively. For performing predictive control over an inflow quantity to a mixing container e. a control unit f is required to have control functions using two loops.
A "Liquid Adjusting Apparatus" and a "Method of Supplying Liquid" are disclosed in Japanese Patent Laid-Open No. 74715/1981 and Japanese Patent Publication No. 163426/1982, respectively. Based on the above-described method and apparatus, flow rates of the plurality of liquids are measured by means of a common measuring device. Liquid supplying means for regulating the flow rates are controlled by independent control loops.
Namely, the flow rates of the liquids differ according to liquid quantities in the supply containers (e.g., for the liquids A and B), flow-rate characteristics of the valve and liquid material properties, and hence the highly precise measurement can not be expected under the same control.
This situation is the same with a tank measuring system, It is required that stop valves of actuators attached to respective systems are controlled by control systems of independent loops. (See Japanese Laid-Open Patent Application Publication Nos. 29114/1982, 163426/1983 and 74715/1981.)
With a view to achieving highly accurate measurement, it has been proposed a method of effecting a change-over i accordance with a predetermined measurement deviation by providing parallel valves having different flow velocities. In this case, however, to perform the control function requires the control of two loops.
The reason why this expression "control functions of two loops" is used herein is that when making use of a dispersive type control unit, two pieces of control units are not necessary, because the measuring process can be done in the single control unit. Judging from the number of inputs and outputs and softwares, however, the two pieces of control units are required.
In a batch producing process, when using a multiplicity of medical liquids, the liquid material properties thereof are different. As a result, it often happens that cumulative measurement can not be performed in the same container. Consequently, there is utilized a production system arranged in such a way that: a plurality of liquid receiving containers are prepared; mixable liquids are measured in the same container;,and unmixable liquids are measured in another container. For this reason, an adjusting tank designed for reaction and adjustment has to be provided on the lower stream side.
In a production system where the adjusting tank for the reaction and adjustment is of a fixed type, when producing multiple liquids, the equipments have to be provided according to classification of the liquids. Especially, the fulfillment of highly accurate measurement requires, as explained earlier, the multiplicity of measurement tanks, the adjusting tank, a pipe measuring device attached to the adjusting tank, the control unit and attached valves. In this case, it follows that the equipments are utilized for some kinds of liquids, but are not used for other kinds of liquids. This system has much futility, thereby increasing the initial costs of the equipments. There is increasingly a demand for a multipurpose production system. In the fixed production system, however, a modification in the piping system is required to be made; and further modification in the attached device thereof is also needed, resulting in still more complicated system.
To simplify the construction, there has recently been proposed a moving type batch production system which permits a reduction in the number of measuring devices. In this batch production system, measurement tank or the adjusting tank is put into a moving type.
Where this system is applied to a conventional measuring device, however, the measuring time differs according to magnitude of a measurement set value. If the measurement set value is large, the measurement takes much time, with the result that restriction is given to a carrier time of capacity in the moving type production system. For this reason, in the prior art production system, a required number of measuring devices are provided so as not to give the restriction to the carrier time. This arrangement contradicts the advantage of the moving type production system. Based on the conventional production system, a stay-time in the station is resultantly further extended. (A remarkable number of measuring devices are needed in terms of conditions such as a range of measurement set value, a limit of measuring time, measuring accuracy and so forth. Hence, an operating time for coupling the pipes and other processes increases).
In a production system designed for photographic photo-sensitive materials, light-shielding properties must be kept because of treating the photo-sensitive materials. An increment in the number of joined portions brings about intricacy of the system, and variations in carrier cycle exerts influences on performance of the products.
In the prior art liquid measuring mixer, the measuring control is carried out on condition that the flow velocity is constant. Hence, the conventional mixer has the defects in measuring accuracy, range and time which have been set forth above.